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TEXBOT 5: Circadian Clocks

TEXBOT5 brings together a diverse collection of perspectives on the theme of the Circadian Clock. All the papers have previously been published in the Journal of Experimental Botany (JXB) and, as a collection, the papers highlight the intricacies and pervasive significance of circadian patterns in physiological and metabolic processes. The collection also celebrates the award to Paul Devlin (author of the first paper in this collection) of a FESPP award for outstanding young plant scientists. Incidentally, this award is sponsored by JXB. Three of the papers in the collection arose from sponsored sessions at the Annual Meeting of the Society for Experimental Biology, the paper by Stitt et al. has been taken from the Special Issue on Inorganic Nitrogen Assimilation published in April 2002, and the Adams et al. paper was submitted and published as a regular review paper.

In his review entitled 'Signs of the time: environmental input to the circadian clock', Devlin discusses the mechanisms of entrainment of circadian rhythms in plants through diurnal light and temperature changes. He cites evidence that indicates that the sensitivity of the circadian system to light is itself clock regulated. A feedback mechanism ensures maximum sensitivity at dawn and dusk through changes in levels of photoreceptor expression and the 'gating or modulation of responsivity to signals from photoreceptors'. The robustness of the system is also illustrated by the entrainment of the clock through temperature fluctuations alongside insensitivity of the period length to temperature.

Carré and Kim in their paper 'MYB transcription factors in the Arabidopsis circadian clock' focus on what is known about molecular mechanisms in the Arabidopsis circadian clock. They suggest, 'The circadian oscillator of Arabidopsis might comprise multiple loops, mediating positive as well as negative feedback'. In the paper entitled 'Steps towards an integrated view of nitrogen metabolism', Stitt et al. review evidence that diurnal patterns in nitrogen metabolism are necessarily subject to multi-layered regulation to facilitate co-ordination with many other metabolic and cellular processes. However some of these patterns are thought to be responsive rather than anticipatory. Dodd et al. in the paper 'Crassulacean acid metabolism: plastic, fantastic' explore the interplay between environmental cues and molecular and biochemical regulation of the CAM cycle.

In the final paper, Adams et al. take an applied perspective and suggest that a much greater physiological understanding of photoperiod sensitivity could help to build more useful quantitative flowering models.